Sesquiterpene and acetogenin derivatives from the marine red alga Laurencia okamurai

Abstract

In addition to 13 known compounds, four new bisabolane sesquiterpenes, okamurenes A-D (1-4), a new chamigrane derivative, okamurene E (5), and a new C₁₂-acetogenin, okamuragenin (6), were isolated from the marine red alga Laurencia okamurai. The structures of these compounds were determined through detailed spectroscopic analyses. Of these, okamurenes A and B (1 and 2) are the first examples of bromobisabolane sesquiterpenes possessing a phenyl moiety among Laurencia-derived sesquiterpenes, while okamuragenin (6) was the first acetogenin aldehyde possessing a C₁₂-carbon skeleton. Each of the isolated compounds was evaluated for the brine shrimp (Artemia salina) lethal assay and 7-hydroxylaurene displayed potent lethality with LD₅₀ 1.8 μM.

Figure 1

Structures of the isolated new compounds 1–6 from L. okamurai.

Figure 2

Key COSY (bold lines) and HMBC (arrows) correlations for compounds 1, 3/4, 5, and 6.

Figure 3

Key NOESY correlations for compounds 1 and 2.